NORMAL-MODE DOUBLE-BRANCH DISPERSION-RELATION FOR METALS WITHIN A VARIATIONAL CALCULATION

In a previous note [1] a variational calculation was considered which describes volume plasmons in high-density metals. We extend this calcu lation by considering a more flexible parametrization and show that, a s a result, a splitting is obtained leading to two normal modes for ea ch value of the transferred momentum q. The single particle excitation s are responsible for the new structure. The strength and the energy o f each mode determine its collective or single particle character for very small or very large values of q. The present results predict an a ppreciable redistribution of transition strength, in agreement with re cent experimental findings.